1. Field of the Invention
The present invention relates to a luminaire and, more particularly, to a medium angle type floodlight which produces a medium beam light with a one-tenth-peak spread of substantially 45.degree.-65.degree..
2. Description of the Prior Art
Floodlights are generally classified according to their applications into narrow angle type, medium angle type, and wide angle type. The medium angle type floodlight luminaire, as described above, has a one-tenth-peak spread of substantially 45.degree.-65.degree. (represented by twice the angle from the optical axis for providing the luminous intensity which is one-tenth of the peak luminous intensity) and may be widely used than the wide angle type floodlight luminaire is used. Medium angle type floodlight luminaires are used, for example, in baseball fields, tennis courts, school grounds, parking lots, and so on. It has been found from experience that the one-tenth-peak spread of the medium angle type floodlight luminaire is preferable within an angle range of about 45.degree.-65.degree. from the perspective of the uniformity of illuminance and the lighting effectiveness.
A reflector for a conventional medium angle type floodlight luminaire is generally made of super pure aluminum and is paraboloid in contour or very close to it. The reflecting surface is processed with a matte finish or with a hammer tone finish consisting of a plurality of substantially hemispherical recesses in its entirety, or is formed to have a plurality of small triangular or rectangular reflecting surface units in its entirety. The reflecting surface is either electrolytically polished or chemically polished. The conventional reflectors of such constructions are insufficient in the one-tenth-peak spread or in the beam factor (the ratio of beam flux within one-tenth-peak spread and the total lamp lumen). For example, with a reflector whose reflecting surface is processed with the matte finish in its entirety, the light falling on the reflector surface is irregularly reflected by the reflecting surface so that a medium beam is obtained. However, the beam factor is lower than that of a specular reflector because of lower reflectance.
The reflector having the reflecting surface processed with the hammer tone finish consisting of the plurality of substantially hemispherical recesses in its entirety has a sufficient specularity that it provides a beam factor as good as that of the above-mentioned reflector. However, with this reflector, it is not possible to obtain a one-tenth-peak spread of over 45.degree. generally. For obtaining a one-tenth-peak spread of substantially 45.degree.-65.degree. with the reflector having the plurality of recesses, the depth of the each recess must be greater than the diameter of the recess on the reflecting surface. This raises the cost of forming projections for making the above recesses in a dies for forming the reflector, increasing the manufacturing cost for the dies and the reflector itself. Further, as the depth of the recesses increases, the actual depth of the recesses of the reflector formed by the dies and the height of the projections formed in the dies tend not to correspond with each other, so that the dimensions of the reflector obtained actually may differ from that of the design. With a recess having still greater depth, the irregular reflection tends to increase in the recess so that the beam factor and the luminaire efficiency are decreased.
With the reflector having the reflecting surface being formed to have the plurality of reflecting surface units in its entirety, the shape of each reflecting surface unit is complex and the number of the units is relatively great. Accordingly, an expensive hydraulic pressing device must be used for forming a plurality of such reflecting surface units at the same time. The use of the hydraulic pressing device leads to a higher manufacturing cost. Further, the plurality of reflecting surface units formed over the entire reflecting surface causes irregular reflection among the reflecting surface units themselves, so that the beam factor and the luminaire efficiency are decreased.